1. Field
The present disclosure relates to a high-sensitivity transparent gas sensor and a method for manufacturing the same. More particularly, the present disclosure relates to a high-sensitivity transparent gas sensor having high light transmittance as well as superior gas sensitivity even when no heat is applied from outside and consuming less power, and a method for manufacturing the same.
2. Description of the Related Art
Gas sensors for detecting toxic gas, explosive gas, environmentally harmful gas, etc. are important in many fields including health care, national defense, counter-terrorism and environment. Researches are consistently ongoing on the gas sensors. In particular, researches are being carried out on the semiconductor gas sensor wherein gas-sensitive metal oxide film is used.
In general, a semiconductor gas sensor comprises a substrate, an electrode formed on the substrate, and a gas-sensing layer formed on the electrode. The substrate is made of silicon or alumina, and the electrode is made of noble metal such as platinum (Pt), gold (Au), etc. And, the gas-sensing layer is made of metal oxide film. The semiconductor gas sensor detects the presence, concentration, etc. of a gas based on the change in electrical resistance of the metal oxide film (gas-sensitive material) resulting from adsorption and oxidation/reduction reaction of the gas on the surface of the metal oxide film. Usually, the gas-sensitive material is a metal oxide semiconductor material such as zinc oxide (ZnO), tin oxide (SnO2), tungsten oxide (WO3) titanium oxide (TiO2), indium oxide (In2O3), etc.
Recently, efforts are being made to improve gas sensitivity by increasing the specific surface area of the gas-sensing layer. For instance, semiconductor gas sensors have been suggested.
Since the semiconductor gas sensor operates on a simple principle, is compact in volume and costs little, it is expected to capable of replacing the existing electrochemical or optical gas sensors.
Furthermore, if a semiconductor gas sensor having high sensitivity for the gas to be detected and consuming less power could be manufactured, it may be mounted on a mobile phone or other mobile devices, thereby further enhancing the functionality of the mobile devices. In addition, if a transparent semiconductor gas sensor could be manufactured, it may be mounted on transparent displays and transparent mobile phones which will be realized in near future as well as on car windowpanes.
However, no transparent gas sensor with excellent light transmittance in the visible region without sacrificing performance has been reported as yet. In addition, despite the many advantages over the electrochemical or optical gas sensors, the existing semiconductor gas sensors are not widely used for practical applications for the following reasons.
First, the semiconductor gas sensor is opaque and expensive. Specifically, since the substrate is made of silicon or alumina and the electrode is made of an opaque noble metal such as platinum (Pt), gold (Au), etc., the gas sensor is not transparent. And, the noble metal such as platinum (Pt) or gold (Au) used in the electrode is expensive. In addition, since the process of forming the electrode (metal layer) and the process of depositing the gas-sensing layer (metal oxide film) is not compatible with each other, large-scale production is difficult.
Further, the gas sensor requires a heat source for operation. That is to say, the existing semiconductor gas sensor has good gas sensitivity only when heat of 200-400° C. is supplied from an external heat source such as a metal heater. Besides, the existing semiconductor gas sensor lacks reliability due to inaccurate change in resistance of the gas-sensitive material because of high contact resistance between the metal (e.g., Pt) of the electrode and the gas-sensing layer (metal oxide film). In addition, it consumes a lot of power. For example, power consumption of a general existing thick-film gas sensor is about 1 mW, and that of a thin-film gas sensor based on microelectromechanical systems (MEMS) is about 10-200 mW. Above all things, since the existing semiconductor gas sensor is opaque, as described above, it is inapplicable to transparent electronic devices such as transparent displays, transparent mobile phones, etc. or transparent products such as windowpanes of cars.